Spatial distribution of ammonia concentrations and modelled dry deposition in an intensive dairy production region

Authors: Leytem, April; WALKER, JOHN - ENVIRONMENTAL PROTECTION AGENCY (EPA); WU, ZHIYONG - RTI INTERNATIONAL, USA; Nouwakpo, Sayjro; BAUBLITZ, COLLEEN - ENVIRONMENTAL PROTECTION AGENCY (EPA); BASH, JESSE - ENVIRONMENTAL PROTECTION AGENCY (EPA); BEACHLEY, GREGORY - ENVIRONMENTAL PROTECTION AGENCY (EPA)

Submitted to: Atmosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2023
Publication Date: 12/22/2023
Citation: Leytem, A.B., Walker, J.T., Wu, Z., Nouwakpo, S.K., Baublitz, C., Bash, J., Beachley, G. 2023. Spatial distribution of ammonia concentrations and modelled dry deposition in an intensive dairy production region. Atmosphere. 15(1):1-23. https://doi.org/10.3390/atmos15010015.
DOI: https://doi.org/10.3390/atmos15010015

Interpretive Summary: Ammonia emissions from agriculture represent ~83% of the total anthropogenic emissions in the U.S. These emissions and resulting deposition into the landscape can generate issues related to human and ecosystem health. This study evaluated the spatial distribution of ammonia emissions across a region characterized by agriculture and intensive dairy production. Peak ammonia concentrations were 4-5 times greater at an intensive dairy site compared to mixed agriculture/dairy or agricultural sites, and 26 times greater than minimal agricultural sites. Temperature was one of the larger drivers of emissions and therefore seasonal trends were prominent at all sites. Elevated ammonia concentrations downwind of dairies result in high rates of ammonia dry deposition to the landscape. Dry deposition rates estimated using a field-scale bi-directional exchange model predict net downward annual fluxes spanning two orders of magnitude across the range of observed air concentrations. Our results indicate that annual dry deposition rates in areas of intensive dairy production can approach 50 kg (nitrogen) N ha/yr, compared to < 1 kg N ha/yr in natural landscapes absent of dairy production and other agriculture. Croplands were found to be net sources of ammonia to the atmosphere after fertilization, particularly during the spring, but take up ammonia from the atmosphere during other periods. Direction of research toward better understanding soil processes is needed to improve understanding of the importance of ammonia dry deposition to arid and sparsely vegetated natural ecosystems across the western U.S. Additionally, work is needed to improve understanding of the role of nitrogen deposition in the health of sagebrush ecosystems, taking into account interactions between disturbance, nitrogen inputs, and changing climate.

Technical Abstract: Agriculture generates ~83% of total U.S. ammonia (NH3) emissions, potentially adversely impacting sensitive ecosystems through wet and dry deposition. Regions with intense livestock production, such as the dairy region of south-central Idaho, generate hotspots of NH3 emissions. Our objective was to measure the spatial and temporal variability of NH3 across this region and estimate its dry deposition. Ambient NH3 was measured using diffusive passive samplers at 8 sites in two transects across the region from 2018-2020. NH3 fluxes were estimated using the Surface Tiled Aerosol and Gaseous Exchange (STAGE) model. Peak NH3 concentrations were 4-5 times greater at a high-density dairy site compared to mixed agriculture/dairy or agricultural sites, and 26 times greater than non-agricultural sites with prominent seasonal trends driven by temperature. Annual estimated dry deposition rates in areas of intensive dairy production can approach 50 kg Nitrogen ha/yr, compared to < 1 kg Nitrogen ha/yr in natural landscapes. Modeling work highlighted a need for better understanding of soil emission potential in environments with high soil pH and low leaf area. Research toward better understanding soil processes is needed to improve understanding of ammonia dry deposition to arid and sparsely vegetated natural ecosystems across the western U.S.